Stepped-lap core for inductive apparatus



Feb. 28, 1961 B. B. ELLIS STEPPED-LAP CORE FOR INDUCTIVE APPARATUS Original Filed D60. 29, 1955 S Sheets-Sheet 1 Fig.|.

INVENTOR Belvin B. Ellis WITNESSES:

ATTORNEY Feb. 28, 1961 B. B. ELLIS 2,973,494

STEPPED-LAP CORE FOR INDUCTIVE-APPARATUS Original Filed Dec. 29, 1955 3 Sheets-Sheet 3 Fig.9. la a Fiq.l0.

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,facture and losses can be reduced by the United States Patent STEPPED-LAP CORE FOR INDUCTIVE APPARATUS Original application Dec. 29, 1955, Ser. No. 556,152.

Divided and this application July 26, 1957, Ser. No. 674,406

8 Claims. (Cl. 336-217) The invention relates, generally, to cores for inductive apparatus and, more particularly, to cores provided with joints adapting them to fit around preformed coils.

This application is a division of applicants parent application filed December 29, 1955, Serial No. 556,152, and assigned to the assignee of the instant application.

In the art, cores having joints to enable them to be applied to preformed coils or the preformed coils applied to them have been utilized with a fair measure of success. However, in cut cores the losses at the joints are high enough to add considerably to the cost of operation of transmission systems, and raise the problem of how to get the losses down.

There are a number of Well-known types of joints in use at the present time. The butt joint in which the flux flows in the laminations passes from end to end at the joint. .Cores having butt joints have served their time well and will continue to be used, but cost of manucore to be described hereinafter.

Another core used employs abutt lap joint. In this. core, a number of laminations are arranged in groups,

and the groups have square end faces. The groups are superimposed on one another with the square ends offset. The square ends of the groups are then fitted together somewhat like a mortise and tenon joint to make a closed loop around a preformed coil. This type of core presents a problem in fitting to get properbutt contact to accommodate an effective flow of the flux and low losses.

There may be some modifications of these cores but they all present'the same problems. Further, they always invite cost reduction. I

Theobject .of *this invention is to provide a low loss nealing the core after preforming all the manufacturing operations that introduce loss producing strains in the magnetic strip from which the core is made.

Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

I The invention accordingly comprises the several steps and. the relation and order of one or more of such steps with respect to each of the others; the apparatus embodying features of; construction, combinations and arrangement of parts adapted to effect such steps, and the article which possesses thecharacteristics, relation .of elements, all as exemplified in the detailed disclosure hereinafter setforth and the scope of the application of which will be indicated in. the claims.

",For a fuller understanding of the nature and objects l of the invention, reference shouldbe had to the following 2,973,494 Patented Feb. 28, 1961 ICC detailed description taken in connection with the accompanying drawings, in which:

Figure l is a view in end elevation of a wound core showing it clamped adjacent a cut;

Fig. 2 is a view in end elevation of the core shown in Fig. l, with the main portion of the core straightened to arrange the laminations in stepped relationship;

Fig. 3 is a view in end elevation of the wound core shown in Fig. 2 curled up to form a substantially circular core with the laminations forming stepped-lap joints;

Fig. 4 is a view in end elevation of a wound and split core showing the laminations separated into groups with the ends disposed in stepped relationship;

Fig. 5 is an end view of a wound core, the laminations of which have been arranged in groups and in stepped relationship to one another and shaped to form a core, the stepped-lap joints of which are wholly within the straight portions of a yoke section of the core;

Fig. 6 is a view in end elevation of a core showing the laminations matching as they are brought end to end;

Fig. 7 is an end view of a wound core with a steppedlap joint, the laminations being arranged in groups of equal numbers of laminations and the core shaped;

Fig. 8 is a view in side elevation of the ends of a core arranged for fitting together to provide a stepped-lap joint;

Fig. 9 is a view partly in section and partly in side elevation of a coil and sections of the core showing how the core may be assembled around the coil;

Fig. 10 is a view partly in section and partly in side elevation of a core and coil showing a stepped-lap joint at the corner of the core; and

' Fig. 11 is a view partly in section and partly in side elevation of a core and coil showing a joint in the leg of the core.

Referring now to the drawings and Fig. 1 in particular, a wound core shown generally at 9 is made by winding a plurality of turns 10 of oriented magnetic strip material on one another. The number of turns of oriented magnetic strip material and the width of the strip will depend on the design and expected capacity of the core 9. The diameter of the core 9 will be to a great extent determinedby the size of the preformed coil or winding 8, with which it is to be utilized.

In order to apply the core to a preformed coil, it is out along a line 11. The direction of the cut, relative to the laminations 10, may be varied to meet the designers objective. Usually the cut will be along the diameter of the core, as shown in Fig. 1. In this embodiment of the invention, the core is illustrated as substantially circular, but suchshape is not necessary as a loop of any suitable shape may be employed.

In order to make a stepped-lap arrangement of the laminations to provide a low loss joint, the laminations are clamped in fixed relationship to one another on one side of the cut 11 bymeans of a clamp 12. After the clamp 12 has been applied, the laminations of the core are straightened out, as shown generally at 13 in Fig. 2.

It will be obvious that the straightening out of the main portion of the core will arrange the laminations 10 in stepped relationship,as shown at 14.

'If it is desired to step the laminations more in one operation than effected by straightening out the group or stack of laminations, they may be bowed or curved in the opposite direction from the curve of the first winding. Other operations of this type may be introduced to acceleratethe making of the core. Such operations will be obvious from the description of the present method.

A second clamp 15 is now applied to the other end of the straight section 13 of the core. The clamp 12 vis released and the straight section of the core 13 curled :up to forma loop, as shown in Fig.3. As the laminaone or two thicknesses of the laminations.

. losses.

tion. 7 V v 'joint may be opened and the laminations fitted through the preformed coil, as for example in Fig. 9, and the of .6 times the thickness of the laminations by repeating the operation twice.

If now the stepped ends of the laminations are fitted together, a series of stepped-lap joints will be formed in the laminations,'as showngenerally at 16. As will be observed, the laminations, which are the same in numher as the turns of the coil, are disposed with each lamination forming a joint which is offsetor staggered relative to the joint in the next adjacent lamination. The end of one lamination laps the end of the next adjacent lamination. Accordingly, the joint comprises a number of laminations, the ends of which are arranged in a stepped order, the end portions of one lamination lapping the end portion of the next lamination forming a joint which may be described as a stepped-lap joint because of the arrangement of the laminations.

In some instances, the ends of the individual laminations may abut one another; however, this is not essential. The ends of the individual laminations may be spaced. Satisfactory results were obtained with the ends of the laminations spaced from one another as much as The lamination ends in one layer should overlap the lamination ends in the next layer by a substantial amount. It has been found in practice that excellent results have been obtained in cores when the lamination ends overlap in the stepped- .lap joint to the extent of about six times the thickness times the thickness, or the ratio of lap to thickness is 1.5 to 1 up to 5 to 1, there is a continuous improvement in both apparent watt (A.W.) losses and true watt (T.W.) The improvement, when plotted, is a linear relationship between A.W. and TV]. Further, it has been found that when the ratio of lap to cross-sectional area of the lamination is greater than 6 to 1, there is very little improvement in both A.W. and T.W. Tests -.1'Ve2lld that when the ratio is 6.to 1, the core generally is within 13% in A.W. and 1% in T.W. of the lossesfof a wound core of the same material and with- .out a joint. Therefore, there ,is little to be gained by increasing the ratio over 6 to 1.

The distance the joint in one lamination will be offset or staggered with relation to thejoint in the next adjacent lamination may be varied appreciably, depending on the design requirements. A very satisfactory core has been produced with joints in adjacent laminations or groups of laminations spaced and the laminations overlapped to a distance of about six times the thickness of the lamination or the build-up of laminations respectively. I

The core may now be clamped at the joint 11 and shaped to conform to the preformed coil to which it is to be applied. Usually the cores are shaped similar to the one shown in Fig. 5. After the core has been shaped, it will be annealed to relieve stresses, in accordancewith some suitable process well known in the art and therefore need not be described.

. The annealing may be performed after the core has been shaped, and no more operations areto be per .formed which will introduce locked-in stresses in the iron of the core and therefore increase the losses in opera- After the core has been shaped and annealed, the

4 laminations fitted together to form the stepped-lap joint described hereinbefore. It has been found that the bending of the laminations to fit them around the coil is not severe enough to so strain the material that the losses in operation are appreciably higher.

When the core has a large number of laminations, the stepped-lap joint forming the main joint may extend through a rather substantial sector of the core.

It has been found desirable in some instances to confine the stepped-lap joints of the individual laminations to the straight section of a yoke or leg. However, in some instances it may be advantageous to make the joint on a corner. When desirable to make the joint in the yoke, the laminations will be arranged in groups, as shown in Fig. 4.

In this particular illustration, there are four groups, 17, 13, 1% and 20, shown. Group 17 has only two laminations; group 18, three; group 19, four; and group each group from the body of the core.

.as many individual laminations as the designer may find preferable for his building operations and final product.

Since the laminations are all of the same gauge, standard jigs and devices may be made which will readily separate the desired number of laminations required for When the laminations have been separated into the groups of the desired size, they may be manipulated in the manner described hereinbefore, either as individual groups, or as a whole, to arrange the individual laminations in stepped relationship. 7

if the groups of laminations are arranged in individual groups to get the required step relationship of the individual laminations, they may be assembled by superimposing the groups on one another in the relationship in which they are wound. If all the groups have been arranged while held together but with the groups kept separated by a jig or other device, then they are ready to be adjusted to locate the joints as desired.

Assuming now that the groups have been arranged to get the laminations 10 in the required stepped relationship as individual groups, then group 18 will be superimposed on group 17 with the stepped-lap joints of the groups substantially aligned. The same practice will be followed with groups 19 and 20. The result is that the stepped-lap joints will all now be located so that when the core is shaped as shown in Fig. 5, the stepped-lap joints will lie within the straight section of the upper yoke of the core. This greatly facilitates the holding of the members making the joint together and results in a low loss joint.

After a core made up of groups of laminations arranged to form stepped-lap joints has been fitted together to form a loop, the core having the stepped-lap joints is clamped and then shaped and annealed as mentioned hereinbefore. Many cores have been assembled in the manner described, and tests have been made to ascertain their efficiency. It has been found that this method of making cores lends itself to factory practice and renders unnecessary many of the expensive operations heretofore required.

It has been demonstrated that it is unnecessary to work the cut ends of the laminations to remove burrs since the burrswill be located in contact with an insulating layer provided on the magnetic strip. Further, during the annealing of the core, many of the burrs will be removed. Experience reveals that the remaining burrs will not cut through the insulation and do not, in any way, cause losses.

The fact that the laminations of the core are not bonded to one another by an adhesive means that when the core has been shapedand annealed, it consists of .a number of reasonably flexible independent laminations or .groups that may be taken apart andfitted through the window in the preformedwindings and the ends of the laminations again matched to form stepped-lap joints,- as shown in Fig. 5. It has been found that the laminations constituting the core may be distorted an amount sufiicient to enable the fitting of them into the preformed coil without setting up any appreciable losses which result from stresses.

The ease and speed with which these cores may be disassembled and fitted through preformed coils lends itself to manufacturing operations. Further, a core manufactured in this way requires only one cut to enable it to be assembled on a preformed coil. Therefore, such a core has only one overall joint to introduce losses. However, it is to be understood that in order to meet design requirements, more than one joint may be provided and the losses will be about in proportion to the number employed.

Another distinct advantage of this type of core is that the laminations do not have to be bonded to one another which greatly cuts the cost of manufacture. Further, a core with laminations free and overlapped as in this invention cuts the sound level during operation very appreciably which is a highly desirable characteristic. Also, submersion in oil dampens the buzzing at the joint and thus attenuates the sound level by or 30 db In order to convey some concept of the low losses and low sound level of this type of core, tests were made and the data obtained is recorded hereinafter:

Stepped-lap joint Sound level dbdt) in oil=33 in ambient of 30".

The cores tested which gave the foregoing results were arranged in the manner illustrated in Fig. 5. In this particular test, the laminations had an overlap joint with a 6 to 1 ratio of spiral length to group build-up. The increased area of the joint, in this instance, 6 times, allowed a 1/6 induction and thus a 1/ 6 reluctance, and as evident from the table, this gave very excellent results. However, it is to be understood that these features may be varied greatly to meet any design requirements.

The test results were so good that the core, while it had a physical joint, gave magnetic results almost equivalent to a core without a physical joint. Of course, there were two contributing features namely, the steppedlap joint and low residual stresses.

In constructing a jointed core, more than one joint may be employed. However, in order to get the low losses, all joints must be stepped-lap joints as described.

Since certain changes in carrying out the above process and certain modifications in the article which embody the invention may be made without departing fro-m its scope, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In a four-sided core, in combination, a plurality of turns of oriented magnetic material, the turns being severed from one another providing laminations with substantially aligned ends, the laminations being arranged in stepped relationship to one another, the aligned ends of one lamination overlapping the aligned ends of the next adjacent lamination presenting a stepped-lap joint joining the ends of the laminations, said stepped joint comprising more than three laminations, the joints of all of said laminations being near the center of one side of said core to provide a single openable joint completely across said core whereby the joint in said coremay be closed by placing the cut ends of said laminations opposite each other in a group comprising more than three laminations, the portion of one lamination overlapping the next lamination being at least 2.5 times the thickness of a lamination.

2. In a core, in combination, a predetermined number of turns of oriented magnetic strip material, the turns of magnetic strip material being cut at a predetermined place and arranged in groups, each group consisting of more than three turns arranged in stepped relationship, the ends of each turn being aligned with one another forming a joint, the joint of one turn being offset from the joint of the next adjacent turn and overlapping the joint of the adjacent turn by a distance at least six times the thickness of an individual turn, all joints of the group of turns being disposed within the same region of the core to provide a single openable joint completely across said core, whereby the turns may be assembled into said core in a group comprising more than three turns and the joint closed.

3. In a wound type core, in combination, a predeter mined number of turns of oriented magnetic strip material wound on one another forming a core, the turns forming the core being cut at a predetermined section to provide independent laminations, the laminations being divided into at least four groups each group comprising more than three laminations, each succeeding group comprising a greater number of laminations than the preceding group, the ends of the laminations being arranged in stepped relationship, each lamination forming a loop, the ends of each lamination being aligned with one another to provide a joint that is offset relative to the joint in the next adjacent lamination thereby forming a series of stepped-lap joints in each group, the groups of laminations being superimposed on one another with the stepped-lap joints of each group being substantially repetitive and the joints in all groups being in the same region of the core to provide a single openable joint completely across said core whereby the laminations may be assembled into said core in a group comprising more than three laminations and the joint closed.

4. In a wound type core, in combination, a plurality of turns of oriented magnetic material, the turns being severed from one another providing laminations with substantially aligned ends, the laminations being arranged in stepped relationship to one another, the aligned ends of one lamination overlapping the aligned ends of the next adjacent lamination and presenting a stepped-lap joint joining the ends of the laminations, each said stepped-lap comprising more than three laminations, the joints of all of said laminations being in the same region in said core to provide a single openable joint completely across said core whereby the turns may be assembled into said core in a group comprising more than three turns and the joint closed, the portion of one lamination overlapping the next lamination being within the limits of from one to six times the thickness of each individual lamination.

5. In a four-sided core, in combination, a predetermined number of turns of oriented magnetic strip material, the turns of magnetic material being cut at a predetermined place and arranged in groups, each group consisting of more than three turns arranged in step rela- V tionship, the ends of each turn being aligned with one another forming a joint, the joint of one turn being oiiset from the joint of the nextadjacent turn to form a stepped-lap joint overlapping the joint in each of the adjacent turns an amount greater than six times the thickness of an individual lamination, the length of the step joint formed by the abutting ends of each group extending through a substantial sector of the core, and with the joints of all of said groups near the center in the same side of said core to provide a single openable 7 joint completely across said core whereby said laminations may be assembled into said core in a groupcomprising more than three laminations and the joint closed;

6. In a core, in combination, a predetermined number of turns of oriented magnetic strip material, the turns of magnetic strip material being cut at a predetermined place and arranged in at least six groups, each group consisting of more than three turns arranged in step relationship, the ends of the stepped turns of each group being in substantial alignment with each other, the stepped joint in each group of turns being of a recurring pattern, the stepped joint formed by the aligned ends of each group of turns being long compared to the thickness of the core and the combined joints of said groups of turns providing a single joint completely across said core whereby the turns may be assembled into said core in a group comprising more than three turns and the joint closed.

7. In a core of substantially rectangular shape having leg portions and yoke portions, a predetermined number of turns of oriented magnetic strip material, the turns of magnetic material being cut in a yoke portion of the core and arranged in groups, each group consisting of more than three turns arranged in stepped relationship, the ends of each turn being aligned with one another forming a joint substantially in the center of a yoke portion of the core, the joint of one turn being offset from the joint of'the next adjacent turn in the order of 1 to 6 times the thickness of each turn to form a stepped joint in the yoke of the core, the stepped joint in each group of turns being of a recurring pattern, said core comprising at least six groups of turns with the stepped joints in said plurality of groups providing a single joint completely across said core whereby the turns may be assembled into said core in a group comprising more than three turns and the joint closed.

8. In a wound type core, in combination, a predetermined number of turns of oriented magnetic strip material, said strips of magnetic material being electrically insulated from each other, the turns of magnetic strip material being cut at a predetermined place and arranged in groups, each group comprising more than three turns having the out ends of each turn substantially aligned with each other, the joint of one turn being offset from the joint of the next adjacent turn by an amount approximately six times the thickness of an individual turn to form a stepped joint in each group of turns, the stepped joint in each group of turns being of a recurring pattern, the length of the stepped joint formed by the aligned ends of each group of turns being substantial compared to the thickness of the core, and the combined stepped joints of said groups of turns providing a single openable joint completely across said core whereby the turns may be assembled into said core in a group comprising more than three turns and the joint closed.

References Cited in the file of this patent UNITED STATES PATENTS 1,935,426 Acly Nov. 14, 1933 2,477,350 Somerville July 26, 1949 2,548,624 Sclater Apr. 10, 1951 2,614,158 Sefton et al. Oct. 14, 1952 2,702,936 Hurt Mar. 1, 1955 FOREIGN PATENTS 1,111,252 France Oct. 26, 1955 

